Overhead doors have been used for many years to secure various enclosures including manufacturing plants, warehouses, garages, and other industrial doorways. It is well known in the art to provide a safety device on the leading edge of these doors to minimize both damage to the doors and potential injury to users when the door is closing. Such safety devices are generally coupled to a door controller. If the safety device encounters an impact, a signal is transmitted to the controller. The signal causes the door to act in a prescribed manner. For example, the controller may cause the door to stop or reverse direction.
Typically, safety edges of the type found in U.S. Pat. No. 3,462,885 to Miller are employed. In particular, the safety edge in Miller is comprised of a resiliently compressible structure. The resilient structure includes a pair of flexible contact strips which are electrically connected to a motor. Upon deflection of the resilient structure, the contact strips engage one another and transmit an electrical signal to the motor, resulting in stoppage or reversal of the door. Alternatively, pneumatically actuated safety edges may be employed. Pneumatically actuated safety edges consist of fluid-filled chambers which are coupled to pressure sensors. The pressure sensors are responsive to pulses or changes in fluid pressure within a chamber. While both of these safety edges assist in preventing damage to the door and provide some degree of safety to the users, there exist inherent limitations in both systems.
Specifically, safety edges such as those found in Miller are less sensitive to impact applied perpendicular to the door body than pneumatically actuated safety edges. Furthermore, safety edges such as those in Miller tend to allow for only minimal door over-travel.
Conversely, pneumatically actuated safety edges tend to be more sensitive to impacts in multiple directions. Pneumatically actuated safety edges, however, are more susceptible to rupture than the safety edges in Miller. For instance, a pneumatically actuated safety edge may receive a puncture or rupture in its fluid-filled chamber. Thus, changes in pressure may not be sensed by the system.
While both of the safety edges discussed above have been met with a reasonable degree of success, the present invention is provided to solve the problems discussed above and other problems, and to provide advantages and aspects not provided by prior doors of this type.